1. Field of Invention
This invention relates to III-nitride light emitting devices with at least one p-type layer in the active region.
2. Description of Related Art
Semiconductor light-emitting devices (LEDs) are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness LEDs capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen with the general formula AlxInyGazN, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61, x+y+z=1, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, or III-nitride substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, a light emitting or active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. The active region is n-type (typically Si-doped or undoped).
In accordance with embodiments of the invention, a III-nitride light emitting device includes an n-type layer, a p-type layer, and an active region capable of emitting light between the p-type layer and the n-type layer. The active region includes at least one additional p-type layer. The p-type layer in the active region may be a quantum well layer or a barrier layer. In some embodiments, both the quantum well layers and the barrier layers in the active region are p-type.
In some embodiments, the p-type layer in the active region has an average dislocation density less than about 5xc3x97108 cmxe2x88x922. Several methods are disclosed for fabricating p-type layers in the active region with low defect densities. First, the device layers may be fabricated on a AlInGaN substrate with low defect density. Second the device layers may be fabricated on a thick AlInGaN layer formed by hydride vapor phase epitaxy. Third, the device layers may be fabricated on an AlInGaN layer formed by epitaxial lateral overgrowth.